A patient in need of cardiac resynchronization can have an implanted device with electrodes to stimulate both ventricles. The device can continuously monitor the patient's heart rhythm and deliver if necessary to the patient's heart electrical impulses to stimulate both the left and right ventricles so as to resynchronize them.
The implanted device applies between the respective moments of stimulation of the left and right ventricles an “interventricular delay” (exchangeably referred to as “VVD” or “DVV”) that can be adjusted to resynchronize the contraction of both ventricles towards optimizing the patient's hemodynamic status.
One of such known implantable devices is a CRT pacemaker disclosed in EP 1108446 A1 and its counterpart U.S. Pat. No. 6,556,866 (both assigned to Sorin CRM, previously known as ELA Medical) that applies between the two ventricular stimulations a variable VVD that can be adjusted to resynchronize the contractions of the ventricles with a fine optimization of the hemodynamic status of the patient.
A simultaneous stimulation of both ventricles is not always optimal, because it does not necessarily lead to a synchronous contraction of both ventricles. This is because, firstly, the conduction delays in the myocardium are not necessarily the same in the right and left ventricles, and may depend on multiple factors and, secondly, the location of the left ventricular lead, whether it is a lead inserted into the coronary sinus or an epicardial lead, can affect the detection of the ventricular contractions as well as the delay in stimulation. It is, therefore, desirable to establish a delay between the two stimuli, to adjust this delay to resynchronize the contractions of the ventricles, and to provide a fine optimization of hemodynamics. The VVD may be set to be zero, positive (the left ventricle is stimulated after the right ventricle), or negative (the right ventricle is stimulated after the left ventricle).
A known CRT device operates in a classical “double chamber” pacing mode in which the device monitors the ventricular activity after a spontaneous (i.e., a detection of an atrial P wave depolarization) or stimulated (i.e., application of an atrial pacing pulse A) atrial event. At the same time, the device starts to count a period called “atrioventricular delay” (exchangeably referred to as “AVD” or “DAV”) such that if no spontaneous ventricular activity (i.e., an R wave) was detected before the end of the delay, the device triggers a stimulation of the ventricle (i.e., application of a ventricular pulse V).
Resynchronization therapy based on stimulation of both ventricles requires selection of operating parameters. These operating parameters are individualized to address myocardial contraction disorders (whether spontaneous or induced by a traditional stimulation) such as dilatation of the cardiac chambers, low ejection fraction, and excessive elongation of the QRS duration.
Some clinical studies have observed dramatic positive results for a patient who has congestive heart failure that did not effectively respond to conventional therapies with the precise adjustment of the operating parameters of CRT therapy according to the patient's condition and specific disorder.
These operating parameters are generally designated as a “stimulation configuration”, a term combining the features related to the stimulation sites (i.e., the physical location of the electrodes and the choice of electrodes, in the case of multisite devices) and the sequence of stimulation (i.e., the order in which the stimulation pulses are applied to the heart on the different selected sites and the time interval between successive pulses).
It is also necessary to reassess these operating parameters after they are established and readjust them, if necessary. Indeed, one of the benefits provided by the CRT therapy is the capability of changing the original configuration and the stimulation setup in the long term.
One of the known techniques for adjusting the CRT stimulation parameters is an echocardiographic assessment that estimates the characteristic timings of the systole, in particular, the timing for the opening of the aortic valve. This procedure, typically implemented in hospitals and by skilled personnel, takes a long time, is expensive to implement, and cannot be applied as often as it would be useful or necessary without interfering with the patient's daily life, despite the expected beneficial effects.
Another difficulty inherent with an echocardiographic assessment is that it requires several successive test patterns of stimulation to determine an optimal AVD for each test pattern. The number of combinations to be tested is, therefore, important, but the assessment procedure involves a complicated, time-consuming, and difficult management and processing of the test results to determine an optimal AVD, therefore it is difficult to be applied as a routine and frequent procedure.
Moreover, even with a full implementation of these echocardiographic assessment procedures, approximately 30% of patients do not respond well to the CRT therapy. Even those 30% of the responding patients suffer serious negative consequences such as lower quality of life, increased hospitalizations related to heart failure, and a reduced life expectancy. Most of the studies now focus on treating this refractory patient population by experimenting with new stimulation configurations, and seeking to optimize the operating parameters, both during and after implementation of the device, by periodic reassessment.
There is, therefore, a need for a technique to evaluate in a simple, rapid, automated, and precise manner, the impact that different CRT therapy operating parameters, including AV and VV delays, so as to optimize the hemodynamic status of a patient.
EP 1736203 A1 and its counterpart U.S. Pat. No. 7,664,547 (both assigned to Sorin CRM, previously known as ELA Medical) describe a CRT device that uses, among other parameters, endocardial acceleration (EA) to determine an optimal pacing configuration at or subsequent to the time of implantation. The endocardial acceleration is measured by an accelerometer integrated in an endocardial lead; for example, as described in EP 0515319 A1 and its counterpart U.S. Pat. No. 5,304,208 (both assigned to Sorin Biomedica Cardio SpA)
Several clinical studies have shown that the endocardial acceleration parameter very accurately and in real time reflects the phenomena related to movements of the heart chamber. It provides comprehensive information on the patient's cardiac mechanics, both during normal operation and poor functioning.
Specifically, EP 1736203 A1 and U.S. Pat. No. 7,664,547, cited above, propose to establish a characteristic relationship between a peak endocardial acceleration (“PEA”) and the AVD for each stimulation configuration selected, by scanning the atrioventricular delay AVD and by recording the variations in the amplitude of peak of endocardial acceleration (PEA), usually the first peak of PEA, i.e., PEA1. This characteristic relationship is determined periodically in a test mode triggered by the implantable device, and the results are processed and combined to give a composite performance index that reflects the effectiveness of the configuration. The different characteristics, more specifically the corresponding indices, are evaluated, and the configuration that maximizes this index (optimal performance index) is chosen. This performance index is derived from the area comprised under the PEA vs. AVD characteristic, and corresponds to the efficiency of the ventricular function.
Another optimization method is described in the article by J M Dupuis, et al.: Programming Optimal Atrioventricular Delay in Dual Chamber Pacing Using Peak Endocardial Acceleration: Comparison with a Standard Echocardiographic Procedure, PACE 2003, 26: [Pt II], 210-213. This technique also describes scanning of the AVD in the considered stimulation configuration to create a PEA vs. AVD characteristic, but the value that leads to the optimal of the AVD is the inflection point of the characteristic. The inflection point corresponds to a period of maximum filling of the ventricle without truncation of the A wave (a minimum delay between the closing of the mitral valve and the beginning of the QRS complex). The corresponding algorithm, although it gives satisfactory results, suffers from requiring several minutes for execution because multiple scans of AVD are required for various VVD values that are separately tested, before the optimal pair {AVD, VVD} is selected.
Another technique, described in U.S. Pat. Pub. No. 2007/0179542 A1 (Medtronic, Inc.) seeks a correlation or a synchronization between the morphologies of the respective EA and intracardiac electrogram (EGM) signals that respectively reflect mechanical (EA) and electrical (EGM) parameters. The analysis of these signals provides an assumed optimal AVD value for a given configuration of stimulation. But the optimization of the VVD parameter requires successive testing of many different configurations and analysis of the obtained results.